, 1997). It has been shown that orientation and direction selectivity are established by different mechanisms. While the initial establishment of orientation selectivity in

cortical neurons is independent of visual experience (see review in White and Fitzpatrick, 2007), several lines of evidence indicate that the emergence of direction selectivity Birinapant in vitro strictly requires visual experience. Thus, direction-preference maps are absent at eye opening and do not develop in ferrets that are reared in darkness (Li et al., 2006). Moreover, visual experience with moving stimuli just after eye opening drives the emergence of direction-selective responses in the ferret visual cortex (Li et al., 2008). However, the connectivity and the mechanisms that are necessary for the emergence of direction selectivity remain unclear. In recent years, rodents and especially mice are becoming an attractive model for the investigation of such mechanisms in vivo. Various transgenic mice lines have been used to study visual system development (Fagiolini Raf inhibitor et al., 2003 and Cang et al.,

2005), plasticity (Fagiolini et al., 2004, Syken et al., 2006 and Wang et al., 2010), and function of specific cell types in the visual cortex (Sohya et al., 2007, Kerlin et al., 2010 and Runyan et al., 2010). It is important to remember that unlike in ferrets, cats, and primates, neurons in the primary visual cortex of rodents are not organized into orientation columns. Instead, orientation-selective neurons are distributed in a mixed “salt-and-pepper” manner throughout the primary visual cortex (Ohki Florfenicol et al., 2005 and Van Hooser et al., 2005). Nevertheless,

highly tuned orientation- and direction-selective neurons have been shown to be abundant in the mouse visual cortex (Dräger, 1975, Métin et al., 1988, Sohya et al., 2007, Niell and Stryker, 2008 and Wang et al., 2010). While the emergence of orientation selectivity has been investigated in the rodent visual cortex (Fagiolini et al., 1994 and Fagiolini et al., 2003), the development of direction selectivity has so far received less attention, except in recent studies that investigated the emergence of direction selectivity at the level of the mouse retina. In mice, retinal ganglion cells exhibit strong direction selectivity (Elstrott et al., 2008 and Yonehara et al., 2009). Remarkably, this strong direction selectivity is already present at eye opening (Elstrott et al., 2008, Chen et al., 2009 and Yonehara et al., 2009). Moreover, robust directional responses have been detected in dark-reared mice and in mice lacking cholinergic retinal waves (Elstrott et al., 2008 and Chen et al., 2009), indicating that visual experience and patterned activity are not required for the development of direction selectivity in the mouse retina.